1. Field of the Invention
The present invention relates to an automatic focusing (AF) apparatus of a camera and particularly to an AF apparatus of a camera, which detects repeatedly in-focus condition through a photographic lens while driving the photographic lens, predicts an in-focus point, namely, a moving amount by which the lens is driven for setting the focusing condition, based on the results of the detections, and drives the photographic lens toward the predicted in-focus point.
2. Description of the Related Art
According to U.S. Pat. No. 4,762,986, it is proposed that if a predicted value for an in-focus point by the so-called hill climbing method differs by more than a prescribed value from an actual value obtained by driving according to the predicted value, prediction control operation is forbidden because the predicted value is regarded as lacking reliability. In addition, in an AF apparatus of a camera, which drives a lens by obtaining an amount of defocus and a defocusing direction by the so-called TTL phase difference system, if an object to be photographed is a moving object, an in-focus point for the moving object is predicted so that the lens is driven, as proposed in U.S. Patent Appln. Ser. No. 936,103 assigned to the same assignee of the present application. According to this apparatus of U.S. Patent Appln. Ser. No. 936,103, moving object determining operation as to whether the object is a moving object or not is not effected in cases in which the defocusing directions detected at the previous time and at the present time are reversed, a value for converting the defocus amount to a lens drive amount is larger than a prescribed value, the defocus amount is larger than a prescribed amount, or a charge accumulation period of a charge coupled device (CCD) for focus detection is longer than a prescribed value.
However, for example if zooming operation is carried out, a size of an image on the focus detection CCD changes considerably or in the case of an object photographed in a large magnification, a small movement of the object causes a large movement on the CCD. As a result, it happens that a correct defocus amount cannot be obtained, making it impossible to predict an in-focus point for the moving object. The above mentioned conventional AF apparatus does not give any disclosure as to the countermeasures. In addition, if focus detection is effected by projection of auxiliary light to an object having a low luminance, a noise component is liable to be superimposed onto an output of the CCD and blur of an image due to the movement of the object cannot be disregarded. Thus, the focus detection precision is lowered and, consequently, the in-focus point for the moving object cannot be predicted.